1. Field of the Invention
The present invention relates to a roller member used for sheet feed or the like and to a sheet feeder and an image forming apparatus which employ such a roller member. Particularly, in a roller member where a rotary shaft is inserted through a through-hole of a roller part and the roller part is removably mounted on a periphery of the rotary shaft, a feature of the invention is that the roller member is adapted to prevent the displacement of the roller part mounted on the periphery of the rotary shaft and to properly retain the roller part at a predetermined position on the rotary shaft.
2. Description of the Related Art
In image forming apparatuses such as copiers and printers, the sheet feeder adapted to feed a sheet by rotating the roller member has conventionally been used for feeding and transporting the sheet such as recording paper from a paper cassette or the like.
A roller body, such as disclosed in Patent Document 1 (Unexamined Patent Publication No. H09-188434), where the roller part is integrally mounted on the periphery of the rotary shaft is used as the above-described roller member. In the case of deterioration or the like of the roller part, the entire roller body is replaced. Alternatively, the above-described roller member may be a separation roller, as disclosed in Patent Document 2 (Unexamined Patent Publication No. 2009-269686), which has a structure where the rotary shaft is inserted through a through-hole of the roller part and the roller part is removably mounted on the periphery of the rotary shaft. In the case of deterioration or the like of the roller part, the roller part is removed from the rotary shaft so that only the roller part is replaced.
It is noted here that the roller body as set forth in the above Patent Document 1 has a problem that when the roller part is deteriorated, the entire roller body is replaced so that the cost increases.
In the case of the separation roller set forth in the above Patent Document 2, the roller part is removably mounted on the periphery of the rotary shaft by engaging a snap fit claw formed on the inside of a core material of the roller part with a groove formed in the periphery of the rotary shaft.
However, in the structure where the roller part is mounted on the periphery of the rotary shaft by simply engaging the snap fit claw formed on the inside of the core material of the roller part with the groove formed in the periphery of the rotary shaft, a gap is produced between the snap fit claw and the groove. This leads to rattling of the roller part mounted on the rotary shaft. Hence, when the sheet such as the recording paper is fed and transported from the paper cassette, the sheet may be shifted, leading to a misfeed.
Therefore, the Patent document 2 proposes a structure where a guide cover is rotatably mounted to one end of the roller part. This guide cover is rotated in a direction to move away from the roller part so as to permit the roller part to be separated from the rotary shaft. On the other hand, after the roller part is mounted on the rotary shaft, this guide cover is rotated toward the roller part so that a control wall disposed at this guide cover can control the axial rattling of the roller part.
However, the provision of the guide cover at the one end of the roller part leads to the increase in the number of parts and thence, to the cost increase. What is more, a space for the guide cover is required so that an apparatus grows in size. Further, the replacement of the roller part requires an operation of rotating the guide cover away from the roller part and separating the roller part from the rotary shaft as described above and an operation of rotating the guide cover toward the roller part after the roller part is mounted on the rotary shaft. The operation of replacing the roller part is cumbersome and takes much time.